1. Technical Field
The present invention relates to a display device for displaying videos including both of moving images and still images.
2. Description of the Related Art
There have been proposed methods for controlling display of display devices for clearly displaying moving images without detracting the lifetime of the display devices. An example of such a method is described in Japanese Patent Kokai No. 10-161629 (hereinafter, referred to as patent document 1). The patent document 1 discloses a cathode-ray tube (CRT) as a display device. Hereinafter, the display device disclosed in the patent document 1 is referred to as a CRT display device.
Conventionally, since a CRT display device for computer has very often displayed still images for a long time, long persistence fluorescent material has been used as fluorescent material for the CRT display device. The long persistence fluorescent material has a characteristic that faint fatigue of the fluorescent material does not remain even when the same position on the fluorescent material is irradiated with an electronic beam. In addition, the brightness of images in the CRT display device for computer is set to be low.
On the other hand, since a CRT display device for television has mainly displayed moving images, short persistence fluorescent material has been used as fluorescent material for the CRT display device for television. The short persistence fluorescent material has a characteristic that an effect of an irradiated beam can be suppressed to a minimum. In addition, since the CRT display device for television mainly displays the moving images, the brightness of images is set to be higher than that of the CRT display device for computer.
Recently, as moving images can be displayed on a CRT display device using a computer, a mixture of still images and moving images can be displayed on the CRT display device. However, a burn-in may occur when the mixture of still images and moving images is displayed on the CRT display device. The burn-in is referred to as a phenomenon that a particular portion of the CRT display device on which the still images are displayed (referred to as a still image region) is exhausted and vestiges of the exhaustion remains in the still image region. When the burn-in occurs, the lifetime of the CRT display device becomes shortened.
Accordingly, the patent document 1 discloses a display control method for controlling output of images for a display device for displaying still images and/or moving images (CRT display device). In this display control method, first, it is determined whether or not an image to be displayed has a still image region. Next, if only a moving image region is present in the image with no still image region, the image is instantly displayed in the display device, and, if both of the moving image region and the still image region are present in the image, after randomly adding black dots in the still image region, the image is displayed in the display device. It is described in the patent document 1 that this method can prevent the burn-in in the still image region.
However, The above-mentioned conventional technique has the following problem. When the moving image region and the still image region are present in the image, even if the black dots are randomly added in the still image region, it does not necessarily follow that the black dots are added in a region of the still image region in which the burn-in is apt to occur. On this account, there is little possibility of significant reduction of the burn-in. Accordingly, viewers may see images having quality deteriorated due to the burn-in in the display device.